Realumination of dealuminated zeolites Y

Tunable hybrid zeolites prepared by partial interconversion

Zeolite interconversion is a widely used strategy due to its unique advantages in the synthesis of some zeolites. By using a long-chain quaternary amine as both a structure-directing agent and porogen, we have produced superior catalysts, which we named Hybrid Zeolites, as their structures are made of building units of different zeolite types. The properties of these materials can be conveniently tuned, and their catalytic performance can be optimized simply by stopping the interconversion at different times. For cracking the 1,3,5-triisopropylbenzene, Hybrid Zeolites made of FAU and MFI units show a 5-fold increase in selectivity towards the desired product, that is, 1,3-diisopropylbenzene, compared to the commercial FAU, and a 7-fold increase in conversion at constant selectivity compared to MFI zeolite.

High-silica hollow Y zeolite by selective desilication of dealuminated NaY crystals in the presence of protective Al species

High-silica hollow faujasite crystals were obtained by dealumination of standard NaY crystals followed by their selective desilication in the presence of protective aluminum species.

Acidity Adjustment of HZSM-5 Zeolites by Dealumination and Realumination with Steaming and Citric Acid Treatments

This article describes a novel method for acidity adjustment of HZSM-5 zeolites with steaming and citric acid treatments and demonstrates the realumination effect of citric acid on HZSM-5 zeolites dealuminated by steaming. A series of modified HZSM-5 zeolites were prepared by streaming and/or acid treatments and characterized by means of X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), (27)Al MAS NMR spectroscopy, hydroxyl infrared spectroscopy (OH-IR), pyridine-adsorbed infrared spectroscopy, and N(2) adsorption in the present investigation. The results showed that compared with single HCl or citric acid treatment, steaming treatment, and steaming/HCl treatments, citric acid treatment after steaming exclusively increased the amount of framework Al due to reinsertion of extraframework Al into the defective sites of the steamed HZSM-5 framework. This realumination effect of the citric acid treatment on the steamed HZSM-5 zeolite, which is reported here for the first time to the best of our knowledge, could nearly recover the pore structure of the steamed zeolite to that of the parent HZSM-5 zeolite and appropriately tailor the amount and strength of different acid sites, which sheds light on optimizing the physicochemical properties of HZSM-5 zeolites. It was also found that the steaming treatment prior to the citric acid treatment was the precondition of the realumination of HZSM-5 zeolites, suggesting that the lattice defect sites generated during steaming were necessary for citric acid to work.